A time to digital converter (TDC) is a circuit block that converts time information to digital signals. It has two major input clock signals, a digitally controlled oscillator (DCO) clock signal and a reference clock signal. A DCO clock signal with high speed of several GHz may pass multi-stages of delay cells.
For a conventional TDC with coarse or fine resolution or resolution amplified by a time amplifier, the finest delay resolution is worse at low voltage, low temperature, or slow corner due to degraded inverter performance. Because a total delay time across all delay cells should be larger than one DCO period to have correct timing conversion, a maximum period of DCO clock is selected. As such, the finest delay resolution is fixed and limited by the maximum period of DCO clock, where the delay time is still much larger than one DCO period as DCO frequency increases several times.
The information disclosed in this Background section is intended only to provide context for various embodiments of the invention described below and, therefore, this Background section may include information that is not necessarily prior art information (i.e., information that is already known to a person of ordinary skill in the art). Thus, work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.